1. Field of the Invention
The present invention relates to a disk player and, more particularly, to a tracking servo apparatus of a disk player.
2. Description of the Prior Art
In a disk player for playing an information recording disk (hereinafter, simply referred to as a disk) such as video disk, digital audio disc, or the like, a tracking servo apparatus is provided to control so as to allow an information reading spot of the pickup to accurately trace a target recording track irrespective of the decentering of the disk or the like.
The tracking servo apparatus performs the position control of the reading spot with respect to the recording track in such a manner that a tracking error signal according to a deviation amount of the information reading spot in the radial direction of the disk from the recording track on the disk is formed and an actuator to shift the information reading point or spot in the disk radial direction is driven in accordance with the tracking error signal. That is, the tracking servo apparatus constructs the so-called closed loop control system. On the other hand, in such a servo apparatus, when executing a jumping operation in which the information reading spot skips a number of recording tracks, the servo loop is opened and a jump pulse is supplied to the actuator and, thereafter, the servo loop is closed at a predetermined timing to thereby execute the servo pull-in operation.
If an obstacle such as a scratch, air bubble, or the like exists on the disk, when a laser beam passes over such an obstacle, an error may result such as a decrease in reflected light amount, loss of focus, or the like occurs. In such a case, if the servo pull-in force is small, the information reading spot is held at a position out of the desired track due to such an obstacle and is not returned to the track but is moved to the preceding track which has already been scanned, and the spot repetitively traces the same track. That is, what is called a groove lock occurs during which the tracking servo does not accurately function.